Crystal clear high barrier packaging film

ABSTRACT

A transparent multilayer coextruded heat shrinkable barrier film is useful for high-value packaging applications such as food and medical device packaging. The transparent multilayer coextruded heat shrinkable barrier film includes first and second outer layers formed using a transparent polyester or polyester copolymer; an inner nanolayer sequence including a plurality of nanolayers a) including ethylene vinyl alcohol, alternating with nanolayers b) including at least one of ethylene ethyl acrylate, low density polyethylene and linear low density polyethylene, each of the nanolayers b) having a degree of crystallinity less than about 45%; and adhesive layers between each of the two outer layers and the inner nanolayer sequence. The film has a light transmittance of at least about 80% and a heat shrunk of at least about ten percent in at least one direction.

RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 17/504,769, filed on Oct. 19, 2021, which in turnclaims priority to U.S. Provisional Application 63/123,588, filed onDec. 10, 2020, the disclosures of which are incorporated by reference.U.S. patent application Ser. No. 17/504,769, filed on Oct. 19, 2021, isalso a continuation-in-part of U.S. patent application Ser. No.17/231,062, filed on Apr. 15, 2021, and the preceding U.S. ProvisionalApplication 63/116,965, filed on Nov. 23, 2020, the disclosures of whichare incorporated by reference. This patent application claims priorityto all of the foregoing applications.

FIELD OF THE INVENTION

This invention is directed to a multilayer coextruded film having bothhigh barrier and high clarity, useful for high-value packagingapplications, and to a multilayer coextruded shrink film having highbarrier and high clarity.

BACKGROUND OF THE INVENTION

Barrier films are commonly used for food and medical packagingapplications that require high resistance to penetration by bothmoisture and oxygen. Barrier films are commonly made by combining layersof low density polyethylene (“LDPE”) or linear low density polyethylene(“LLDPE”), which provide moisture barrier, with layers of polyamide(“PA”) and/or ethylene vinyl alcohol (“EVOH”), which provide oxygenbarrier. The oxygen barrier materials are hygroscopic and self-absorbmoisture from the air, which in turn lowers their oxygen barrierproperties. For this reason, the barrier films are usually constructedwith the oxygen barrier layer(s) in the center, surrounded and protectedby the moisture barrier layers, and joined to the moisture barrierlayers using known polymer-based adhesive resins. For example, onesimple barrier film structure has the following basic layer sequence:LDPE/Adhesive/EVOH/Adhesive/LDPE. Barrier films can also have athickness and integrity that renders them thermoformable for theproduction of barrier containers.

Conventional layer combinations used to provide high barrier to moistureand oxygen often do not provide films with high transparency andclarity. The relative lack of transparency and clarity can result inpackages that appear hazy and/or compromised to the consumer and canmake the product contained in the package to appear compromised as well.Especially with high-value medical and food packages, it is important tomaintain the perception that the product contained therein is clean,fresh and free of blemishes or contamination. There is a need or desirefor food and medical packages that provide high barrier to moisture andoxygen without distorting or diminishing the images of the productscontained therein.

SUMMARY OF THE INVENTION

The invention is directed to a high barrier, high transparencymultilayer coextruded film that is useful for packaging foods, medicalsupplies, and other items where high-end performance is desired. Theinvention is also directed to a high barrier, high transparency,multilayer coextruded shrink film formed by stretch orienting the highbarrier, high transparency multilayer coextruded film, and heatshrinkable and heat shrunk packages formed from the shrink film.

The transparent barrier film of the invention combines the high moisturebarrier performance of selected ethylene polymers with the high gasbarrier performance of ethylene vinyl alcohol in a manner that utilizesa novel selection of low crystallinity layer polymers and filmprocessing conditions to optimize the degree of transparency throughoutthe film. The resulting high barrier packaging film suitably has adegree of transparency of at least about 80% or higher, measured usingASTM D1746. The high barrier, high transparency shrink film can beformed by stretch orienting the barrier film, for example using a vacuumthermoforming process, and by allowing the stretched (e.g.,thermoformed) barrier film to cool in the stretched condition. Thestretch oriented film can then be used to form a package, such as athermoformed package, and can be heated to above the glass transitiontemperature of the lower melting layer or layers to cause shrinkage ofthe film around the packaged product.

In one embodiment, the invention is directed to a transparent multilayercoextruded barrier film for use in packaging, which includes:

first and second outer layers formed using a transparent amorphouspolymer;

an inner nanolayer sequence including a plurality of nanolayers a)including ethylene vinyl alcohol, alternating with a plurality ofnanolayers b) including at least one of ethylene ethyl acrylate,ethylene acrylic acid, low density polyethylene and linear low densitypolyethylene, each of the nanolayers b) having a degree of crystallinityless than about 45%; and

adhesive layers between each of the first and second outer layers andthe inner nanolayer sequence;

wherein the film has a light transmittance of at least about 80%.

In another embodiment, the invention is directed to a transparentmultilayer coextruded barrier film for use in packaging, which includes:

first and second outer layers formed using a polyester copolymer;

an inner nanolayer sequence including a plurality of nanolayers a)including ethylene vinyl alcohol, alternating with nanolayers b)including at least one of ethylene ethyl acrylate and ethylene acrylicacid, and

adhesive layers between each of the two outer layers and the innernanolayer sequence.

In another embodiment, the invention is directed to a transparentmultilayer coextruded barrier film for use in packaging, which includes:

first and second outer layers formed using a transparent amorphouspolymer;

a first inner nanolayer sequence including at least three nanolayers a)including ethylene vinyl alcohol, alternating with at least threenanolayers b) including an adhesive, each of the nanolayers b) having adegree of crystallinity less than about 45%;

adhesive layers between each of the two outer layers and the first innernanolayer sequence; and

a second inner nanolayer sequence including at least three nanolayers c)including a first low density polyethylene or linear low densitypolyethylene, alternating with at least three nanolayers d) including asecond low density polyethylene or linear low density polyethylene,wherein each of the nanolayers c) and d) has a degree of crystallinityless than about 45%.

In another embodiment, the invention is directed to a transparentmultilayer coextruded heat shrinkable barrier film for use in packaging,which includes:

first and second outer layers formed using a transparent amorphouspolymer;

an inner nanolayer sequence including a plurality of nanolayers a)including ethylene vinyl alcohol, alternating with a plurality ofnanolayers b) including at least one of ethylene ethyl acrylate,ethylene acrylic acid, low density polyethylene and linear low densitypolyethylene, each of the nanolayers b) having a degree of crystallinityless than about 45%; and

adhesive layers between each of the first and second outer layers andthe inner nanolayer sequence;

wherein the film has a light transmittance of at least about 80% and aheat shrink of at least about 10 percent in at least one direction.

In another embodiment, the invention is directed to a transparentmultilayer coextruded heat shrinkable barrier package, which includestwo opposing film segments joined at respective edges, each film segmentcomprising:

first and second outer layers formed using a polyester copolymer;

an inner nanolayer sequence including a plurality of nanolayers a)including ethylene vinyl alcohol, alternating with nanolayers b)including at least one of ethylene ethyl acrylate and ethylene acrylicacid, and

adhesive layers between each of the two outer layers and the innernanolayer sequence;

wherein the heat shrinkable package has a light transmittance of atleast about 80% and a heat shrink of at least about 10 percent in atleast one direction.

In another embodiment, the invention is directed to a method of making atransparent multilayer coextruded heat shrinkable barrier package, whichincludes the steps of:

providing a film including first and second outer layers formed using apolyester copolymer, an inner nanolayer sequence including a pluralityof nanolayers a) including ethylene vinyl alcohol, alternating withnanolayers b) including at least one of ethylene ethyl acrylate andethylene acrylic acid, and adhesive layers between each of the two outerlayers and the inner nanolayer sequence;

stretch orienting the film in at least one direction to form a stretchoriented film;

placing a product between two segments of the stretch oriented film; and

vacuum sealing the segments of the stretch oriented film atcorresponding edges of the segments to form the transparent multilayercoextruded heat shrinkable barrier package;

wherein the heat shrinkable package has a light transmittance of atleast about 80% and a heat shrink of at least about 10 percent in atleast one direction.

In order to achieve optimal transparency, the multilayer coextrudedbarrier film can be produced by a blown film process as described hereinthat utilizes a selection of highly transparent polymers and layerarrangement in a multilayer nanolayer blown film. Alternatively, or inaddition to the foregoing, the multilayer coextruded barrier film can bemade using a rapid quench process, for example, a water coolingapparatus including a wet porous material in direct contact with theblown film bubble and surrounding an outer circumference of the bubble.The wet porous material continuously wipes the outer circumference ofthe bubble with water as the bubble moves along the traveling path,providing the blown film with uniform and rapid quenching for optimaltransparency. Notwithstanding the foregoing, the water cooling apparatusmay not be needed to achieve the desired film transparency if a novelselection of nanolayer polymers and layer arrangement are employed, asdescribed further in this specification.

The transparent multilayer coextruded heat shrinkable barrier film canbe produced by stretch orienting the transparent multilayer coextrudedbarrier film in one or more directions. The orientation of the film canbe accomplished using a vacuum thermoforming process, a nip rollerprocess, an inline orientation tenter frame, or another orientationapparatus that stretches the film in one or more directions and allowsthe film to cool in the stretched state, thereby temporarily “lockingin” the orientation of the polymer molecules in one or more layers. Theorientation can be performed by stretching the film in one moredirections at a temperature that exceeds the glass transitiontemperature T_(g) of the polymer(s) in one or more of the film layersand is typically performed between about 185° F. (85° C.) and about 400°F. (205° C.). “Monoaxial orientation” typically refers to stretchorientation on the machine direction of the film. “Biaxial orientation”typically refers to mutually perpendicular orientations in both themachine and transverse directions. Vacuum thermoforming, by its nature,typically stretches the film in the machine and transverse directions,and at angles that lie in between the machine and transverse directions.

The transparent multilayer coextruded heat shrinkable barrier packagecan be produced by forming two opposing segments of the heat shrinkablebarrier film, sometimes referred to as “halves,” and placing a product(for example, a food or medical product) in between the segments. Thecombination can then be placed in a vacuum and heat sealed at the edgesto form the transparent multilayer coextruded heat shrinkable barrierpackage. The sealed heat shrinkable barrier package can then be heatedto a temperature above the glass transition temperature of one or moreof the polymer layers, whereupon the polymer molecules return towardtheir original unoriented molecular state as the film shrinks to form atransparent multilayer coextruded heat shrunk barrier package. Becauseof its excellent transparency and high barrier properties, the heatshrunk barrier package can be used to contain and store varioushigh-value food and medical products for which an attractive appearanceis important to the purchaser.

With the foregoing in mind, it is a feature and advantage of theinvention to provide a transparent multilayer coextruded barrier filmthat combines high barrier properties with high transparency for use inhigh-value applications, including without limitation high valuepackaging applications for food and medical devices.

It is also a feature and advantage of the invention to provide atransparent multilayer coextruded barrier film that can be thermoformedand used to provide transparent high-barrier containers for use inhigh-value applications, including without limitation high valuepackaging applications for food and medical devices.

It is also a feature and advantage of the invention to provide a heatshrinkable transparent multilayer coextruded barrier film that combineshigh barrier properties with high transparency for use in high-valuepackaging applications.

It is also a feature and advantage of the invention to provide a heatshrinkable transparent multilayer coextruded barrier package thatcombines high barrier properties with high transparency for thepackaging of high-value products, such as food and medical products.

The foregoing and other features and advantages of the invention willbecome further apparent from the following detailed description of theinvention, read in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of one example of a transparentmultilayer coextruded barrier film of the invention that includes 30nanolayers.

FIG. 2 is a schematic diagram of one example of a blown film line usefulto make the high barrier, high transparency multilayer coextruded filmsof the invention, which is an upward blown film line.

FIG. 3 is an enlarged schematic diagram of the portion of the blown filmline of FIG. 1 that illustrates a water cooling apparatus used foroptimal clarity.

FIG. 4 is a schematic diagram of a process used to convert a stretchoriented transparent multilayer coextruded barrier film into a heatshrinkable transparent multilayer coextruded barrier package and acorresponding heat shrunk transparent multilayer coextruded barrierpackage.

DETAILED DESCRIPTION OF THE INVENTION

The transparent multilayer coextruded barrier film of the inventionemploys a combination of optimal material and layer selection andoptimal processing to yield a film that has a high level of transparencyin addition to excellent barrier to penetration by oxygen and moisture.The nature and importance of the special processing needed to achievetransparency, varies with the selection of polymers and layerarrangement. When optimal film transparency and barrier properties canbe achieved through the selection of polymers and layer arrangement, thespecial processing, namely rapid quenching in the form of waterquenching, may not be needed. When special processing via the waterquenching process described herein is employed, the polymers and layerarrangement can be varied by a certain amount from what is consideredoptimal, and the optimal transparency can still be achieved. Forpurposes of this disclosure, “optimal transparency” or “hightransparency” refers to barrier films having a light transmittance of atleast about 80%, suitably at least about 84%, or at least about 88%,measured using ASTM D1746.

Multilayer barrier films that can achieve high transparency withoutrequiring special processing include select nanolayer films that includepolyethylene terephthalate glycol (PETG) as one or both of the outerlayers. PETG is both highly transparent and has excellent heat sealproperties. In order for the overall film to have high transparency, itis especially important that one or both outer layers have hightransparency and do not possess haze or other surface properties thatwould inhibit the percent light transmittance of the overall film. PETGis amorphous, having a glass transition temperature of about 80° C. Theamorphous nature of PETG not only renders the affected outer layer(s)clear but contributes to making the entire film clear. PETG is alsothermoformable and contributes to the thermoformability of the entirefilm. For enhanced thermoformability, PETG can also be used in one ormore inner layers of the barrier film.

Other amorphous polymers that can be used as outer film layers to renderinner film layers (and thus, the overall film) clearer include withoutlimitation other amorphous polyesters, polystyrene and polystyrenecopolymers, polycarbonate, and transparent acrylic polymers. In general,the selected polymers should have a low crystallinity and a transparencymeasured as a light transmittance of at least about 80%, or at leastabout 84%, or at least about 88% determined according to ASTM D1746.While the transparent outer layers can improve the transparency of theoverall film by eliminating any haze resulting from surface roughness ofadjacent inner layers, it is also desirable to design the inner layerswith the maximum possible transparency. This can be accomplished usingnanolayers as described below, in which every functional layer (e.g.,every gas barrier layer and every moisture barrier layer) is adjacent toanother layer that improves the transparency of the functional layer.

The transparent, coextruded multilayer barrier film can also include atleast one gas barrier layer or layer combination, and at least onemoisture barrier layer or layer combination. The gas barrier layer orlayer combination can include ethylene-vinyl alcohol (EVOH), which hasgained worldwide recognition for its barrier properties against permeantgases such as oxygen, carbon dioxide and nitrogen. The excellent barrierproperties of EVOH can be attributed to the intermolecular andintramolecular bonding caused by the polar hydroxyl groups in the vinylalcohol units. However, EVOH absorbs water and the water absorptionweakens those bonds, causing a decrease in the gas barrier properties.For this reason, EVOH layers in a barrier film should be sandwichedbetween and protected by moisture barrier layers. For optimaltransparency and protection from moisture, the EVOH can be present inmultiple nanolayers alternating with relatively transparent, amorphous,low crystallinity moisture barrier nanolayers that also serve asadhesive layers. Ethylene ethyl acrylate (EEA) and ethylene acrylic acid(EAA) are examples of two such moisture barrier polymers that can alsoserve as adhesive layers. Other suitable moisture barrier nanolayersthat provide excellent adhesion between adjacent EVOH nanolayers includeblends of EEA or EAA with an anhydride-grafted polyethylene, forexample, a modified polyethylene sold under the name PLEXAR®. Suchadhesive blends can include from about 10% to about 90% by weight EEA orEAA and about 10% to about 90% by weight anhydride-modifiedpolyethylene, or about 25% to about 75% by weight EEA or EAA and about25% to about 75% by weight anhydride-modified polyethylene, or about 40%to about 60% by weight EEA or EAA and about 40% to about 60% by weightanhydride-modified polyethylene, or about 50% by weight EEA or EAA andabout 50% by weight anhydride-modified polyethylene.

In one embodiment, the transparent, coextruded multilayer barrier filmcan include a gas barrier nanolayer combination that includes “x”nanolayers of EVOH alternating with nanolayers of adhesive, wherein theadhesive nanolayers are formed of EEA, EAA, a combination of EEA andEAA, or a combination of EEA or EAA with an anhydride-modifiedpolyethylene. For example, the gas barrier nanolayer combination, whichis located inside the transparent, multilayer coextruded barrier film,can include the following sequence of layers:

-   -   (adhesive/EVOH)_(x)/adhesive

where “x” can be at least 3, or at least 4, or at least 5, or at least6, or at least 7, or at least 8, or at least 9, or at least 10, or atleast 15, or at least 20, or at least 25, or at least 30, or at least35, or at least 40, or at least 45, or at least 50.

The moisture barrier layer or layer combination can also include atleast one primary moisture barrier layer or layer combination thatprovides the film with overall excellent moisture barrier properties, aswell as structural integrity. In order to preserve film clarity, themoisture barrier layer or layer combination can include a first lowdensity polyethylene or linear low density polyethylene having lowcrystallinity, suitably less than about 45%, or less than about 40%,and/or in a range of about 35% to about 40%. The low density or linearlow density polyethylene can have a density of about 0.910 to about0.925 grams/cm³ and can be present as moisture barrier nanolayers. Inone embodiment, the nanolayers formed of the first low density or linearlow density polyethylene can alternate with nanolayers formed of asecond low density or linear low density polyethylene. The second lowdensity polyethylene or linear low density polyethylene can also havelow crystallinity, suitably less than about 45%, or less than about 40%,and/or in a range of about 35% to about 40%. The second low density orlinear low density polyethylene can have a density of about 0.910 toabout 0.925 grams/cm³. The alternating nanolayers of first and secondlow crystallinity low density or linear low density polyethylene furthercontribute high transparency to the multilayer coextruded barrier film,along with moisture barrier, strength, and integrity.

In one embodiment, the transparent, coextruded multilayer barrier filmcan include a moisture barrier nanolayer combination that includes “y”nanolayers of the first low density or linear low density polyethylene(“polyethylene₁”) alternating with nanolayers of the second low densityor linear low density polyethylene (“polyethylene₂”). For example, themoisture barrier nanolayer combination, which can be located inside thetransparent, multilayer coextruded barrier film, can include thefollowing sequence of layers:

-   -   (ployethylene₁/polyethylene₂)_(y)

where “y” can be at least 3, or at least 4, or at least 5, or at least6, or at least 7, or at least 8, or at least 9, or at least 10, or atleast 15, or at least 20, or at least 25, or at least 30, or at least35, or at least 40, or at least 45, or at least 50.

In one embodiment, the gas barrier nanolayer combination can be combinedwith the moisture barrier nanolayer combination to provide atransparent, coextruded multilayer barrier film that includes amorphouspolymer (“AP”) outer layers for excellent transparency, heat sealabilityand thermoformability, and EEA or EAA adhesive (or one of the foregoingadhesive combinations) joining the nanolayer combinations to each otherand to the outer layers. For example, the transparent, coextrudedmultilayer barrier film can include the foregoing sequence of layers:

-   -   AP/(EEA or EAA)/moisture barrier nanolayer combination/gas        barrier nanolayer combination/AP

where the amorphous polymers (AP) are selected from amorphous polyestercopolymer (e.g., PETG), polystyrene, polystyrene copolymers,polycarbonate, amorphous acrylic polymers and copolymers, andcombinations thereof, and are selected to have a light transmittance ofat least about 80%, or at least about 84%, or at least about 88%.

Referring to FIG. 1 , an exemplary multilayer coextruded film 10includes first and second outer layers 12 and 14 which can be formedusing an amorphous polymer or polymer combination. Suitable amorphouspolymers include those having a light transmittance of at least about80%, or at least about 84%, or at least about 88%, measured using ASTMD1746. Suitable amorphous polymers that can meet these requirementsinclude without limitation selected amorphous polyester homopolymer orcopolymer, polystyrene, polystyrene copolymers, polycarbonate, amorphousacrylic polymers and copolymers, and combinations thereof, and areselected to have a light transmittance of at least about 80%, or atleast about 84%, or at least about 88%. Of these, some of the moreamorphous copolymers (for example, PETG) can achieve the desired lighttransmittance without employing the special water quenching techniquesdescribed below. Otherwise, the stated light transmittance should not beregarded as an inherent property of the listed polymers and copolymers.Many of them may require the special processing described below toachieve the desired transparency, as measured by light transmittance.

Suitable polyester homopolymers include without limitation polyethyleneterephthalate, polybutylene terephthalate, and combinations thereof.Polyester homopolymers provide excellent transparency but are generallynot heat sealable. In order to provide the film with heat sealability,one or both of the outer layers can be formed using a polyestercopolymer. Suitable polyester copolymers include without limitationpolyethylene terephthalate glycol, polyethyleneterephthalate-1,4-cyclohexane-2 methyl ester, polyester-polyether blockcopolymers, and combinations thereof. Polyethylene terephthalate glycol(PETG) is particularly suitable for one or both of the outer layers 12and 14 because it provides excellent heat sealability and transparency.For optimal transparency, the polyester copolymer can have a degree ofcrystallinity of less than about 20%, suitably less than about 15%,measured using ASTM D1505. The outer layers 12 and 14, and other filmlayers described below, should be as thin as possible in order toprovide the multilayer coextruded film 10 with maximum transparency. Theouter layers 12 and 14 can be nanolayers or microlayers. The term“nanolayers” refers to film layers having thicknesses in the submicronrange, typically between about 1 to about 999 nanometers, or about 10 toabout 500 nanometers. The term “microlayers” refers to layers havingthicknesses of about 1 to about 999 microns, or about 5 to about 500microns, or about 10 to about 100 microns.

The multilayer coextruded film 10 can also include first and secondadhesive tie layers 16 and 18 between the outer layers 12 and 14 and theinner nanolayer sequence(s) described below. The first and secondadhesive tie layers can be formed of a soft polymer that exhibitstackiness without compromising film clarity. Suitable soft polymersinclude without limitation ethylene methyl acrylate, ethylene ethylacrylate, ethylene acrylic acid, ethylene methacrylic acid, andcombinations thereof. Ethylene ethyl acrylate and ethylene acrylic acidare particularly suitable for one or both of the adhesive tie layers 16and 18 because of their low crystallinity and high clarity. Theforegoing adhesives can also be blended with other adhesive materials,such as chemically-modified polyolefins, provided that the desiredclarity can be maintained. Suitable chemically-modified polyolefinsinclude without limitation anhydride-modified polyethylene, for example,low density or linear low density polyethylene grafted with maleicanhydride. Examples of suitable chemically-modified polyolefins includethose sold under the name PLEXAR® sold by MSI Technology. Thechemically-modified polyolefin can improve the adhesion between thepolyester homopolymer or copolymer outer layers and the ethylene-vinylalcohol in the first inner nanolayer sequence described below. Theadhesive tie layers can suitably be nanolayers having only the thicknessneeded to ensure adequate bonding between adjacent layers.

The multilayer coextruded film 10 also includes at least a first innernanolayer sequence 20 that provides the film 10 with oxygen barrierproperties. The first inner nanolayer sequence includes at least one andsuitably a plurality of oxygen barrier nanolayers includingethylene-vinyl alcohol (EVOH). In the illustrated embodiment, the firstinner nanolayer sequence 20 includes a plurality of nanolayers a) thatinclude EVOH, shown as layers 22, 24 and 26. The nanolayers a) alternatewith a plurality of nanolayers b), shown as layers 28, 30 and 32. Thenanolayers b) can include at least one of ethylene-ethyl acrylate,ethylene acrylic acid, low density polyethylene and linear low densitypolyethylene, and should have a degree of crystallinity less than 45%,suitably less than about 40% in order to provide maximum transparency.When the layers b) are formed using ethylene-ethyl acrylate or ethyleneacrylic acid, they inherently have low crystallinity and hightransparency as explained above. When the nanolayers b) are formed usinglow density polyethylene or linear low density polyethylene, thematerials should be selected to have a crystallinity at the lower end ofthe conventional range for optimal clarity. Low density and linear lowdensity polyethylene typically have crystallinities ranging from about35% to about 60%. When used as the layers b), the low density or linearlow density polyethylene should be selected to have a crystallinity atthe lower end of the normal range, suitably about 35% to about 45%, orabout 35% to about 40%, and should have a density of about 0.910 toabout 0.925 grams/cm³. The nanolayers b) can also include an amount ofanhydride-grafted polyolefin (described above) to provide betteradhesion between the nanolayers b) and the EVOH in the nanolayers a).

When the nanolayers b) are formed of low density or linear low densitypolyethylene, they provide the multilayer coextruded film 10 withadditional moisture barrier, strength and integrity. When the densityand crystallinity of these materials are sufficiently low as describedabove, the nanolayers b) can also provide sufficient adhesion betweenthe EVOH layers for some applications. In one alternative embodiment(not illustrated), additional nanolayers ab) formed of an adhesive tieresin can be positioned between the nanolayers a) and b) to providebetter bonding strength. The nanolayers ab) can be formed of any of theadhesive materials described above and can suitably includeethylene-ethyl acrylate or ethylene acrylic acid, alone or blended withan anhydride-grafted polyolefin. The first inner nanolayer sequence 20can include any suitable number of alternating nanolayers a) and b) and(if appropriate) intervening nanolayers ab). For example, the firstnanolayer sequence may include at least three nanolayers a), or at leastfour nanolayers a), or at least five nanolayers a), or at least sixnanolayers a), or at least seven nanolayers a), or at least eightnanolayers a), or at least nine nanolayers a), or at least tennanolayers a), or at least 15 nanolayers a), or at least 20 nanolayersa), or at least 25 nanolayers a), or at least 30 nanolayers a), or atleast 35 nanolayers a), or at least 40 nanolayers a), or at least 45nanolayers a), or at least 50 nanolayers a). The nanolayers a) mayalternate with at least three nanolayers b), or at least four nanolayersb), or at least five nanolayers b), or at least six nanolayers b), or atleast seven nanolayers b), or at least eight nanolayers b), or at leastnine nanolayers b), or at least ten nanolayers b), or at least 15nanolayers b), or at least 20 nanolayers b), or at least 25 nanolayersb), or at least 30 nanolayers b), or at least 35 nanolayers b), or atleast 40 nanolayers b), or at least 45 nanolayers b), or at least 50nanolayers b).

In one embodiment, the first nanolayer sequence includes layers a) thatinclude EVOH alternating with layers b) that include at least one ofethylene-ethyl acrylate and ethylene acrylic acid. in this embodiment,the multilayer coextruded film 10 can further include a second innernanolayer sequence 40 as shown in FIG. 1 . The second inner nanolayersequence 40 can be designed to provide the film 10 with improvedmoisture barrier and structural integrity and can include a plurality ofnanolayers c) alternating with a plurality of nanolayers d). Thenanolayers c) can include a first low density polyethylene or linear lowdensity polyethylene having low crystallinity, suitably less than about45%, or less than about 40%, and/or in a range of about 35% to about40%. The low density or linear low density polyethylene can have adensity of about 0.910 to about 0.925 grams/cm³. The nanolayers d) caninclude a second low density polyethylene or linear low densitypolyethylene having low crystallinity, suitably less than about 45%, orless than about 40%, and/or in a range of about 35% to about 40%. Thelow density or linear low density polyethylene can have a density ofabout 0.910 to about 0.925 grams/cm³. The alternating nanolayers offirst and second low crystallinity low density or linear low densitypolyethylene further contribute high transparency to the multilayercoextruded barrier film, along with moisture barrier, strength andintegrity.

The second inner nanolayer sequence 40 can include any suitable numberof alternating nanolayers c) and d) and (if appropriate) interveningnanolayers cd) (not shown). For example, the second nanolayer sequencemay include at least three nanolayers c), or at least four nanolayersc), or at least five nanolayers c), or at least six nanolayers c), or atleast seven nanolayers c), or at least eight nanolayers c), or at leastnine nanolayers c), or at least ten nanolayers c), or at least 15nanolayers c), or at least 20 nanolayers c), or at least 25 nanolayersc), or at least 30 nanolayers c), or at least 35 nanolayers c), or atleast 40 nanolayers c), or at least 45 nanolayers c), or at least 50nanolayers c). The nanolayers c) may alternate with a correspondingnumber of nanolayers d), for example, at least three nanolayers d), orat least four nanolayers d), or at least five nanolayers d), or at leastsix nanolayers d), or at least seven nanolayers d), or at least eightnanolayers d), or at least nine nanolayers d), or at least tennanolayers d), or at least 15 nanolayers d), or at least 20 nanolayersd), or at least 25 nanolayers d), or at least 30 nanolayers d), or atleast 35 nanolayers d), or at least 40 nanolayers d), or at least 45nanolayers d), or at least 50 nanolayers d). In the embodimentillustrated in FIG. 1 , the second nanolayer sequence 40 includes tennanolayers c) identified as nanolayers 42, 44, 46, 48, 50, 52, 54, 56,58 and 60, alternating with ten nanolayers d) identified as nanolayers62, 64, 66, 68, 70, 72, 74, 76, 78 and 80.

The nanolayers in the first and second nanolayer sequences 20 and 40 aredesigned to produce a transparent, high barrier multilayer coextrudedfilm 10 for high-end packaging applications, including withoutlimitation the packaging of food and medical devices. Film clarity is ameasure of percent light transmittance and can be measured using ASTMD1746. For example, when a film is exposed to 100% of an incident lightsource, the transmittance is 100% minus (percent absorption+percentreflection). For optimal performance and appearance, the high barriermultilayer coextruded film 10 should have a light transmittance of atleast about 80%, suitably at least about 84%, or at least about 88%.

On order to ensure optimal transparency, the high barrier multilayercoextruded packaging film 10 can be manufactured using an upward ordownward blown film coextrusion process that includes a rapid quenchwater cooling ring as described in U.S. Publication 2020/0298459,published to Schirmer on Sep. 24, 2020, the disclosure of which isincorporated by reference. The operation of the water quenchingapparatus is briefly described below with respect to FIGS. 2 and 3 andis described in more detail in the foregoing publication.

Referring to FIGS. 2 and 3 , a blown film line 110 includes a suitablenumber of extruders 112, each supplied with plastic resin using a hopper114. Each extruder 112 melts the associated plastic resin, heats theresin to a desired extrusion temperature, and feeds it to an annular die116 that is configured to produce a blown film bubble 118 (correspondingto the high barrier multilayer coextruded packaging film 10) having thedesired number of layers. The annular die 116 extrudes the blown filmbubble 118 in a direction of travel 120 toward a collapsing frame 122and a plurality of nip rollers 124. A pressure tube 126, positionedbelow the annular die 116, employs air pressure to inflate the interiorof the blown film bubble 118. The blown film line 110 may be mounted forstability to an upright frame 128.

An air cooling apparatus 130, mounted in the vicinity of the annular die116, includes an air cooling ring 132 that supplies cooling air througha plurality of air vents 134. The air cooling apparatus 130 cools theblown film bubble 118, which is initially molten, to a lower temperaturethat is closer to its solidification point which appears at the frostline 138 along the direction of travel 120. A water cooling apparatus140 is provided in the vicinity of the frost line 38, downstream fromthe air cooling apparatus 130 in the direction of travel 120, andbetween the air cooling apparatus 30 and the nip rollers 124. The watercooling apparatus 140 includes a wet porous material 142 positioned fordirect contact with the blown film bubble 118 and surrounding an outercircumference 144 of the blown film bubble 118, so that the wet porousmaterial 142 continuously wipes the outer circumference 144 of the blownfilm bubble 118 with water as the blown film bubble 118 moves along thetravelling path 120. The wet porous material 142, upon contact with theblown film bubble 118, causes immediate and uniform further cooling ofthe blown film bubble 118. This rapid and uniform cooling results in amore uniform frost line 138 and a more uniform stretching and thicknessof the multilayer blown film and provides the blown film with uniformand optimal clarity.

The wet porous material 142 can be any porous material that is capableof transmitting water through its thickness. The wet porous material 142can be a cloth or screen and is suitably a mesh screen. In oneembodiment, the water cooling apparatus 140 further includes a rigidporous backing 46 supporting the wet porous material 142. In analternative embodiment, a soft porous material such as one made ofpolyester fibers or terry cloth can be stitched or otherwisemechanically attached to a mesh screen cylindrical backing using nylonthreads or another suitable means of attachment, whereupon thecombination of the soft material and mesh screen serves as the wetporous material.

The wet porous material 142 can be maintained in a uniform wet state bysupplying an atomized water/air spray mixture to an outside surface 148of the wet porous material 142. The atomized water/air spray mixture issupplied from a pipe 150 connected to a source 154 and feeds a manifold152. The manifold 152 can be a single manifold that is circular andsurrounds the entire outside surface 48 of an upper portion 156 of thewet porous material 142. Use of a single circular manifold 152, withuniformly spaced spray openings, permits an even distribution of thewater/air spray mixture around the circumference of the wet porousmaterial 142. The manifold 152 can be positioned inside a housing 58,which can be cylindrical and can enclose the wet porous material 142 and(if used) the rigid support backing 146. The housing 158 includes adivider 160 that separates an upper chamber 162 of the housing 158 froma lower chamber 164 of the housing 158. The atomized water/air spraymixture is applied continuously in the upper chamber 162 toward theupper portion 156 of the wet porous material 142 as shown.

Some of the water applied to the wet porous material 142 flows downwarddue to gravity into the lower portion 166 of the wet porous material 142located in the lower chamber 164. The completely wetted porous material142 contacts the exterior surface of the blown film bubble 118 as itmoves in the direction of travel 120. The effects of this continuouscontact are to complete the quenching of the blown film bubble 118 so asto maximize its transparency, while limiting its diameter and blow-upratio. By controlling the quenching and diameter of the blown filmbubble 118 in this fashion, the thickness of the blown film is alsocontrolled more uniformly around the circumference of the blown filmbubble 118, thereby reducing or eliminating thickness disparities.

Excess water can be removed from the lower portion 166 of the wet porousmaterial 142 by applying a vacuum to the lower chamber 164 using avacuum suction device 170, such as a vacuum pump, connected to an outlet172 leading from the lower chamber 168. The vacuum suction device 170removes any excess water from the wet porous material so as to maintainthe floor and surrounding area in a dry state. Excess water thus removedcan be recycled back into the source 154 that supplies the atomizedwater/air mixture.

The uniformly quenched and sized blown film bubble 118 then passes tothe collapsing frame 122 and nip rollers 124, where the bubble 118 iscollapsed into a flat film 174. The flat film 174 may be slit on bothsides and separated using a slitting apparatus (not shown) to producethe high barrier multilayer coextruded packaging film 10.

Special coextrusion die equipment can also be employed to produce thehigh barrier multilayer coextruded packaging film 10 as shown anddescribed herein. Suitable die equipment for producing this and othercoextruded multilayer blown films having complex nanolayer structures isdescribed in U.S. Pat. No. 11,090,853, issued Aug. 17, 2021, entitled“Modular Disk Coextrusion Die with Opposing Disk Arrangement” andlisting Henry Schirmer as the sole inventor. This patent is incorporatedby reference. The patent describes and claims a blown film coextrusiondie formed using a plurality of cells of thin annular disks that arestacked on top of each other. Each cell includes a central routing diskhaving at least one flow opening, a first sub-cell on a first side ofthe central routing disk, and a second sub-cell on a second side of thecentral routing disk. Each first sub-cell includes a first distributiondisk, a first transition disk and a first spreader disk. Each secondsub-cell includes a second distribution disk, a second transition diskand a second spreader disk arranged in opposite order to the firstsub-cell. Each distribution disk includes a distribution inlet opening,a plurality of outlet openings, and a plurality of channels connectingthe distribution inlet opening with the plurality of outlet openings.Within each cell, the distribution inlet opening in the firstdistribution disk is about 180 degrees opposed to the distribution inletopening in the second distribution disk.

The opposing disk arrangement enables each cell to produce twonanolayers using oppositely oriented sub-cells that balance the meltstreams and pressures and enable the production of very thin uniformlayers. The cells and disks within them can be arranged to produce amultilayer coextruded film having a large number of nanolayers and usingup to twelve different polymer melt streams, enabling production ofcomplex multilayer nanolayer blown films. Further details of the modulardisk coextrusion die with the opposing disk arrangement are provided inthe foregoing patent application.

The transparent multilayer coextruded multilayer film described in anyof the foregoing embodiments can be rendered heat shrinkable by stretchorienting the film in one or more directions using known orientationequipment such as nip rollers, tenter frames, vacuum thermoforming, andother conventional techniques. Uniaxial orientation of the film in themachine direction of the film can be accomplished by stretching the filmbetween two or more successive pairs of nip rollers, wherein eachsuccessive pair of nip rollers has a surface velocity that is greaterthat the surface velocity of the immediately preceding pair. Orientationof the film in the transverse direction can be accomplished using atenter frame that stretches the film in the transverse direction as thefilm moves forward in a direction of travel. Biaxial orientation of thefilm in two mutually perpendicular directions can be accomplished bycombining the foregoing techniques. Vacuum thermoforming can be used tostretch orient the film in multiple directions simultaneously by pullingthe film, or segments of the film, into the shape of a formed package.

Stretch orienting can be performed at a temperature that is above theglass transition temperature of the lowest melting layer and below theglass transition temperature of the highest melting layer. For example,when the film includes one or both outer layers of PETG, which has aglass transition temperature of about 185° F. (85° C.) and one or moreinner layers of EVOH having a glass transition temperature of about 400°F. (205° C.), the stretch orientation can be performed at between thesetwo temperatures. The stretching increases the dimension of the film inthe one or more directions of stretching, from a first originaldimension to a second, larger stretched dimension, and orients thepolymer molecules in the film layers. The film is cooled while beingmaintained in the stretched state, causing it to maintain the second,larger dimension in the one or more directions of stretching. Theresulting heat shrinkable film (“shrink film”) can be later heatedwithout the stretching force and caused to “heat shrink” toward itsinitial, unstretched dimensions.

The amount of heat shrink can be measured using standard testprocedures, including ASTM D2838-18. Using this test, the transparentmultilayer heat shrinkable barrier film can have a heat shrink of atleast about 10% in at least one direction, or at least about 15% in atleast one direction, or at least about 20% in at least one direction, orat least about 25% in at least one direction, or at least about 30% inat least one direction. If the film is biaxially stretched in twomutually perpendicular directions such as in the machine and transversedirections, then it may have a heat shrink of at least about 10% in twomutually perpendicular directions, or at least about 15% in two mutuallyperpendicular directions, or at least about 20% in two mutuallyperpendicular directions, or at least about 25% in two mutuallyperpendicular directions, or at least about 30% in two mutuallyperpendicular directions. The maximum amount of heat shrink generallycorrelates with the amount of stretching used to produce the stretchoriented film. Heat shrinking reduces the stretch orientation byallowing the film to retract towards its initial pre-stretcheddimensions in the absence of a stretching force.

The transparent multilayer heat shrinkable barrier film thus formed canbe formed into segments used to form a package. Two opposing segments,which can be thermoformed into appropriate shapes, can be used to form atransparent multilayer coextruded heat shrinkable barrier package thatmaintains the transparency and the high barrier properties of the film.A product, for example a high value food or medical product, can bepositioned in between the two opposing segments, which are sometimesreferred to as “halves” The halves can be previously uniaxially orbiaxially oriented, and/or thermoformed into a shape, as explainedabove. The opposing segments can then be heat sealed at their respectiveedges, suitably in the presence of a vacuum, to form a sealed packagethat is free of oxygen and air. The sealed package can then be heated inthe absence of a stretching force at a temperature up to the originalstretching temperature, causing the molecular orientations to relax,whereupon the film segments or halves retract and shrink toward theiroriginal unstretched dimensions.

FIG. 4 shows an exemplary process 200 for forming a transparentmultilayer coextruded heat shrinkable barrier package and acorresponding heat shrunk barrier package from a transparent multilayercoextruded heat shrinkable barrier film of the invention. A product 212,which can be a medical or food product, is positioned between twostretch-oriented (e.g., thermoformed) film segments shown in side viewas upper half 214 and lower half 216 at station 218 to form acombination 220. The resulting combination 220 is moved to a vacuumsealing station 222, where the edges of the opposing film segments 214and 216 are heat sealed together using one or more heat sealers 226 inthe presence of vacuum to form sealed edges 217 and 219, therebyenclosing the film segments 214 and 216 around the product 212 andforming the transparent multilayer coextruded heat shrinkable barrierpackage 224. The heat shrinkable barrier package 224 can then be heatedin the absence of a stretching force at the sealing station 222 and/or aseparate downstream heating station to a temperature above the glasstransition temperature of the lowest melting layer and up to theoriginal stretch orienting temperature of the film segments 214 and 216to relax the molecular orientation in the polymer layers and shrink thefilm as shown. Because no stretching force is applied at this stage, theheating causes the sealed and stretched film segments 214 and 216 toretract and shrink toward, or at least closer to, their originalunstretched dimensions to form a tightly shrink wrapped product. Theresulting transparent multilayer coextruded heat shrunk barrier packages228 maintain the high transparency and barrier properties of theoriginal multilayer coextruded barrier film, resulting in a highlyattractive and visually appealing packaged product.

The embodiments of the invention described herein are exemplary. Variousmodifications and improvements can be made without departing from thespirit and scope of the invention. The scope of the invention isindicated by the appended claims, and all changes that fall within themeaning and range of equivalents are intended to be embraced therein.

I claim:
 1. A transparent multilayer coextruded heat shrinkable barrierfilm for use in packaging, comprising: first and second outer layersformed using a transparent amorphous polymer; an inner nanolayersequence including at least three nanolayers a) including ethylene vinylalcohol, alternating with at least three nanolayers b) including atleast one of ethylene ethyl acrylate and ethylene acrylic acid, each ofthe nanolayers b) having a degree of crystallinity less than about 45%;and adhesive nanolayers including at least one of ethylene ethylacrylate and ethylene acrylic acid between each of the first and secondouter layers and the inner nanolayer sequence; wherein the film has alight transmittance of at least about 80% and a heat shrink of at leastabout ten percent in at least one direction and the transparentamorphous polymer in each of the first and second outer layers comprisesan amorphous polyester copolymer.
 2. The transparent multilayercoextruded heat shrinkable barrier film of claim 1, wherein the film hasa heat shrink of at least about ten percent in at least two mutuallyperpendicular directions.
 3. The transparent multilayer coextruded heatshrinkable barrier film of claim 1, wherein the film has a heat shrinkof at least about 20 percent in at least one direction.
 4. Thetransparent multilayer coextruded heat shrinkable barrier film of claim3, wherein the film has a heat shrink of at least about 20 percent in atleast two mutually perpendicular directions.
 5. The transparentmultilayer coextruded heat shrinkable barrier film of claim 1, whereinthe film is rendered heat shrinkable by stretch orientation.
 6. Thetransparent multilayer coextruded heat shrinkable barrier film of claim1, wherein the film is rendered heat shrinkable by vacuum thermoforming.7. The transparent multilayer coextruded heat shrinkable barrier film ofclaim 1, wherein the inner nanolayer sequence comprises at least five ofthe nanolayers a) and at least five of the nanolayers b).
 8. Thetransparent multilayer coextruded heat shrinkable barrier film of claim1, wherein the nanolayers b) have a degree of crystallinity less thanabout 20%.
 9. The transparent multilayer coextruded heat shrinkablebarrier film of claim 8, wherein the nanolayers b) have a degree ofcrystallinity less than about 15%.
 10. The transparent multilayercoextruded heat shrinkable barrier film of claim 1, wherein thenanolayers b) further comprise at least one of low density polyethyleneand linear low density polyethylene and have a degree of crystallinityless than about 40%.
 11. The transparent multilayer coextruded heatshrinkable barrier film of claim 1, wherein the film has a lighttransmission of at least about 84%.
 12. The transparent multilayercoextruded heat shrinkable barrier film of claim 1, wherein the film hasa light transmission of at least about 88%.
 13. The transparentmultilayer coextruded heat shrinkable barrier film of claim 1, whereinthe amorphous polyester copolymer comprises polyethylene terephthalateglycol.
 14. The transparent multilayer coextruded heat shrinkablebarrier film of claim 1, wherein the amorphous polymer in at least oneof the first and second outer layers further comprises at least one ofan amorphous polystyrene or polystyrene copolymer, a polycarbonate, andan amorphous acrylic polymer.
 15. The transparent multilayer coextrudedheat shrinkable barrier film of claim 1, wherein the adhesive nanolayersbetween each of the first and second outer layers and the innernanolayer sequence further comprise an anhydride-grafted polyolefin. 16.The transparent multilayer coextruded heat shrinkable barrier film ofclaim 1, further comprising a second inner nanolayer sequence includinga plurality of nanolayers c) including a first low density polyethyleneor linear low density polyethylene, alternating with nanolayers d)including a second low density polyethylene or linear low densitypolyethylene, wherein each of the nanolayers c) and d) has a degree ofcrystallinity less than about 45%.
 17. The transparent multilayercoextruded heat shrinkable barrier film of claim 16, wherein each of thenanolayers c) and d) has a degree of crystallinity less than about 40%.18. A transparent multilayer coextruded heat shrinkable barrier package,including two opposing film segments joined at edges of each filmsegment, each film segment comprising: first and second outer layersformed using a polyester copolymer; an inner nanolayer sequenceincluding at least three nanolayers a) including ethylene vinyl alcohol,alternating with at least three nanolayers b) including at least one ofethylene ethyl acrylate and ethylene acrylic acid; and adhesivenanolayers including at least one of ethylene ethyl acrylate andethylene acrylic acid between each of the first and second outer layersand the inner nanolayer sequence; wherein the transparent multilayercoextruded heat shrinkable barrier package has a light transmittance ofat least about 80% and a heat shrinkage of at least about 10% in atleast one direction and the transparent amorphous polymer in each of thefirst and second outer layers comprises an amorphous polyestercopolymer.
 19. The transparent multilayer coextruded heat shrinkablebarrier package of claim 18, wherein at least one of the first andsecond outer layers comprises polyethylene terephthalate glycol.
 20. Thetransparent multilayer coextruded heat shrinkable barrier package ofclaim 18, wherein the heat shrinkage is at least about 25% in at leastone direction.
 21. The transparent multilayer coextruded heat shrinkablebarrier package of claim 18, wherein each film segment further comprisesa second inner nanolayer sequence including a plurality of nanolayers c)including a first low density polyethylene or linear low densitypolyethylene, alternating with nanolayers d) including a second lowdensity polyethylene or linear low density polyethylene, wherein each ofthe nanolayers c) and d) has a degree of crystallinity less than about45%.
 22. A transparent multilayer coextruded heat shrinkable barrierpackage, including two opposing film segments joined at edges of eachfilm segment, each film segment comprising: first and second outerlayers formed using polyethylene terephthalate glycol; an innernanolayer sequence including at least three nanolayers a) includingethylene vinyl alcohol, alternating with at least three nanolayers b)including at least one of ethylene ethyl acrylate and ethylene acrylicacid; and adhesive nanolayers including at least one of ethylene ethylacrylate and ethylene acrylic acid between each of the first and secondouter layers and the inner nanolayer sequence; wherein the transparentmultilayer coextruded heat shrinkable barrier package has a lighttransmittance of at least about 88% and a heat shrinkage of at leastabout 20% in at least one direction and the transparent amorphouspolymer in each of the first and second outer layers comprises anamorphous polyester copolymer.